Electromagnetic radiation is steadily increasing in daily life because the electromagnetic spectrum being used is moving to a higher frequency band, due to increasing multifunctionality and miniaturization of electrical and electronic products and the development of information and communication equipment. Because of this phenomenon, the electromagnetic spectrum radiated from certain sources may cause malfunctions and system errors in surrounding devices and may also damage the human body, such as inducing fever. Therefore, there is increasing demand for EMI shielding technology, which can effectively prevent these problems.
Conventionally, EMI shielding technologies use metal instruments or metal painted or plated conductive membranes. However, if a metal instrument has a complex pattern, processability can deteriorate and the weight of the metal instrument can increase. Further, plating technologies can require complex processes, such as grease removal, etching, neutralizing, activating, accelerating, metalizing, activating, first plating, second plating, and third plating steps, which can impact productivity.
In contrast, electrical conducting and EMI shielding materials using polymer composite resins may have an advantage in terms of production cost and processability, because composite resin products can be produced by injection molding processes.
EMI (Electromagnetic Interference) Shielding Effectiveness may be represented by the following expression:Shielding Effectiveness (S.E.)=R+A+B 
wherein R is surface reflection of electromagnetic radiation, A is internal absorption of electromagnetic radiation, and B is loss caused by multi-reflection.
In the case of metal materials, EMI shielding effectiveness due to surface reflection of electromagnetic radiation can be high because of the higher conductivity (lower impedance) of metal materials. In order to increase the EMI shielding effectiveness of a resin composite, filler having high magnetic permeability can be used. Fillers with high magnetic permeability can increase electrical conductivity and surface reflection and also increase absorption of electromagnetic radiation.
U.S. Pat. No. 5,827,997 discloses a metal-coated carbon filament, for example a nickel coated carbon filament, prepared by an electroplating method, and a composite material including the same. Also, U.S. Publication No. 2002/0108699 discloses conductive fibers impregnated with a wetting agent and including a thermoplastic or thermoset sheath.